Techniques for the liquid storage of platelets for transfusion will be evaluated. Initially, we will concentrate on developing a uniformly successful system for storage at 22 degrees Centigrade beyond 24 hours and on the efficacy of platelets stored at 4 degrees Centigrade. Techniques for detecting antiplatelet factors and antibodies will be developed and contrasted in a variety of disease states. Clinically applicable methods for distinguishing among a variety of thrombocytopenic states will be explored with emphasis on platelet size measurements.